Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$39.85	8.261%	$43.142	$43.14	$43.15	$43.10
Purchase #2	$156.27	12.829%	$176.3179	$176.32	$176.30	$176.30
Purchase #3	$30.78	11.588%	$34.3468	$34.35	$34.35	$34.30
Purchase #4	$146.55	4.422%	$153.0304	$153.03	$153.05	$153.00
Purchase #5	$242.53	12.687%	$273.2998	$273.30	$273.30	$273.30
Purchase #6	$206.99	11.784%	$231.3817	$231.38	$231.40	$231.40
Purchase #7	$99.75	9.375%	$109.1016	$109.10	$109.10	$109.10
7 purchase totals =	$922.72		$1,020.6202	$1,020.62	$1,020.65	$1,020.50